Perforated interlocking slab

ABSTRACT

A perforated interlocking concrete slab, for example moulded from cement, intended for use for example for consolidating turfed areas or sloping banks, has an outline which includes portions that project and portions that are withdrawn with respect to a notional base line that forms a rectangle with sides twice as long as its ends are wide; the projections and withdrawn portions being arranged so that it is possible to lay against half the length of a side of the slab (regarded as extending from a corner) another like slab oriented at will either with its end abutting that half length or with half the length of its side abutting that half length, so that by their interengagement relative displacement longitudinally with respect to that half length is prevented; the perforations passing from the face to the back of the slab and being disposed in first rows that extend parallel to each other and in second rows that extend at right angles to the first rows and parallel to each other, the first and second rows extending obliquely with respect to the rectangular base line. The first rows of perforations can extend in the same direction as the diagonal of the rectangular base line (one of the first rows being situated on that diagonal). Recesses at the corners and midway of the longitudinal sides, combine in an array of such slabs to form perforations of like shape and area as the perforations of the slab.

United States Patent n91 Jordan et al.

[ PERFORATED INTERLOCKING SLAB {75] Inventors: Reinhard Jordan, Baden-Baden;

Fritz Von Langsdorff. Forch, both of Germany [73] Assignee: F. von Langsdorff Bauverfahren Gmbl-l, Rastaat, Germany 22 Filed: Oct. 21, 1974 [211 Appl' No.: 516,146

[30] Foreign Application Priority Data Oct, 31, 1973 Germany n 2354600 [52] [1.8. Ci 404/41; 404/41 X [51] Int. Cl. l. E0l 5/00 [58] Field of Search 404/41, 42, 34; 52/596, 52/609 l 56] References Cited UNITED STATES PATENTS 1.621103 3/27 Fulton 404/41 X 1,974130 9/1934 Wedberg 404/4l X 2,493,470 1/1950 Tau 404/41 X 3,301.148 1/1967 Schraudenbach 404/41 X FOREIGN PATENTS OR APPLICATIONS 1,509,003 1/1968 France 404/41 6,513.546 4/1966 Netherlands. 404/4i 2,010,330 9/1971 Germany i i i ,1 404/41 1,912 l55 11/1970 Germany i, 404/41 Primary ExaminerNile C. Byers, Jr. Attorney, Agent, or FirmAlbert Cl Johnston [57} ABSTRACT A perforated interlocking concrete slah for example moulded from cement. intended for use for example for consolidating turfed areas or sloping hanks. has an outline which includes portions that project and portions that are withdrawn with respect to a notional base line that forms a rectangle with sides twice as long as its ends are wide; the projections and with drawn portions being arranged so that it is possible to lay against half the length of a side of the slab (regarded as extending from a corner) another like slab oriented at will either with its end abutting that half length or with half the length of its side abutting that half length. so that by their interengagement relative displacement longitudinally with respect to that half length is prevented; the perforations passing from the face to the back of the slab and being disposed in first rows that extend parallel to each other and in second rows that extend at right angles to the first rows and parallel to each other, the first and second rows extending obliquely with respect to the rectangular base line The first rows of perforations can extend in the same direction as the diagonal of the rectangular base line (one of the first rows being situated on that diagorial). Recesses at the corners and midway of the longitudinal sides, combine in an array of such slabs to form perforations of like shape and area as the perforations of the slab.

16 Claims. 6 Drawing Figures Sheet 1 of 5 3,923,410

US. Patent Dec. 2, 1975 U.S. Patent Dec. 2, 1975 Sheet 2 of5 3,923,410

US. Patent Dec. 2, 1975 Sheet 3 of5 3,923,410

US. Patent Dec. 2, 1975 Sheet 4 of5 3,923,410

U.S. Patent Dec. 2, 1975 Sheet 5 of5 Fig.6

Fig. 5

PERFORATED INTERLOCKING SLAB BACKGROUND OF THE INVENTION This invention relates to perforated interlocking slabs (which term is used herein to include structural elements and cladding and paving elements in the nature of blocks, bricks, stones, flags and the like) made for example of cement and is applicable particularly though not exclusively to slabs intended for consolidation of turfed areas or sloping banks, e.g. fire engine access ways, garage drives, parking plots etc.

DESCRIPTION OF THE PRIOR ART An interlocking slab provided with perforations is already known whose outline is of corrugated shape. However, the slab cannot be laid in a herringbone formation. Owing to the repeat of the outline corrugations, it is also not possible to lay the slabs in such a formation that a further slab can be laid against a longitudinal side of a first slab with an offset of half the slab length. In this slab, the perforations were arranged in first rows and second rows which were each parallel to one another; the first rows and second rows were at an angle of about 60 and were arranged at an inclination relative to the outline of the slab. If against one of these slabs a neighbouring slab is laid with an orientation 90 different from that of the first mentioned slab, the direction of the rows is changed where the slabs abut. The selected arrangement of perforations also has the result that they are arranged in each case in a line ex tending parallel relative to the longitudinal side and the transverse end of the slabs, entailing disadvantages (mentioned below).

A perforated interlocking slab is also known which is twice as long as it is wide. The slab also has such an outline that it can be laid in a herringbone formation. In this slab, the perforations are also arranged in first rows and second rows which are parallel to one another; these rows cross at right angles and extend parallel to the longitudinal sides and transverse ends of the slab.

The slabs with which the invention is concerned are often laid on areas which have straight boundary edges, for example garage drives, parking places, fire engine ramps and the like. Consequently the slabs are usually laid with their longitudinal sides or transverse ends parallel to those straight edges. Consequently if the rows of perforations extend parallel to the longitudinal sides and/or parallel to the transverse ends of the slabs, numerous disadvantages result when wheeled vehicles are driven over or parked on a covered area, parallel to or at right angles to its straight boundary edge.

SUMMARY OF THE INVENTION The invention provides a perforated interlocking slab comprising in combination a face and a back bounded by an outline, said outline having portions that project and portions that are withdrawn with respect to a notional base line that forms a rectangle with opposite sides twice as long as its opposite ends are wide; said projections and withdrawn portions forming a matching pattern on said opposite ends and a matching pattern on each half length (regarded as extending from a comer) of said opposite sides of the slab whereby another like slab selectively oriented with its end abutting said half length and oriented with half the length of its side abutting said half length as may be desired interengages with said half length to prevent relative displacement longitudinally with respect to said half length; said perforations passing from said face to said back of the slab and being disposed in first rows that extend parallel to each other and in second rows that extend at right angles to said first rows and parallel to each other, said first and second rows extending obliquely with respect to said rectangular base line. The term rows" of course refers to lines in which the perforations are separated by narrower rather than wider webs.

In a preferred form the outline of the slab includes straight line portions extending in zig-zag fashion relatively to the base line. These straight line portions preferably form right angles with one another at the corners of the slabs. Between the corners the straight line portions preferably intersect at obtuse angles. Preferably the angle of intersection of the straight line portions with the base line is the same throughout. In another preferred form the sides and ends of the slab are corrugated. Preferably all the projections and withdrawn portions project or are set back from the base line by the same distances (and also preferably the recesses mentioned below are recessed by constant distances when present).

According to a preferred further feature of the invention the first rows extend in the same direction as the diagonal of the rectangular base line, one of the first rows preferably being situated on the diagonal. With this orientation of the rows, using specific outline shapes, the perforations can be distributed in a particularly advantageous manner over the slab surface.

It is advantageous to construct the slabs in such a manner that the first rows extend parallel to first straight portions of the slab outline. More particularly if the second rows are also situated parallel to second straight portions of the slab outline, an advantageous distribution of perforations is obtained which is adapted to the slab outline.

A particularly close distribution of perforations over the area covered with such slabs is obtained if the slab outline includes one or more recesses of which the area as seen in plan is equivalent to part of the area of a perforation. Advantageously the location of the recess or recesses is in the perforation rows. Preferably the area of the or each recess is equivalent to one half or one quarter of the area of a perforation. The individual recesses can be of different sizes.

According to a preferred feature of the slabs, the or each recess is so disposed that when the slab is laid in abutment with one or more other like slabs, adjacent recesses of neighbouring slabs combine to form a gap akin to a perforation. It is particularly advantageous if all the recesses are supplemented by adjacent recesses of adjacent slabs to fonn perforations. As a result, when a structure or formation is completed using such slabs, the recesses are substantially no longer recognisable as such.

To obtain an attractive appearance and to give the slab or the entire formation, good load-bearing properties, it is advantageous if the perforations form a pattern. preferably if the pattern is continued from slab to slab in the formation. It is particularly advantageous to arrange the slab so that the first and/or second rows are continued in the formation from slab to slab.

In the interests of uniform strangth the webs between the perforations have the same width in the row direction. Preferably also the webs between the perforations nearest the outline and the recess-free outline at this region have half the width of the webs between perforations in the row direction. In this way a formation is obtained which is particularly pleasing in appearance and has good load-bearing properties, since the width of the webs between perforations is constant over the entire formation.

As perforation shapes it is preferred to use perforations which are round, circular, polygonal or square in their basic plan. these being also particularly easy to produce. Naturally, on the other hand, substantially any basic shapes can be used for the perforations.

As regards the shape of the perforations, in the direction from the face to the back of the slab, it is preferable to use prismatic perforations. that is to say perforations of constant cross-section over the height of the slab, or perforations which widen towards the face of the block. In the latter case the anchorage of the slab to the foundation or subsoil is improved when grass grows and a greater concentration of material is obtained in the lower region of the slab, which can be advantageous for obtaining a secure position. But in some cases it may also be advantageous to widen the perforations towards the back of the slab, for example in order to allow grass roots to spread out more easily when the slabs are used as lawn slabs.

To have a simple shape for producing the slabs it is preferable for the perforations all to be of the same shape. On the other hand, however, it is also possible to modify the shape of the perforations in a regular or irregular manner, for example in order to provide perforations which are more suitable for the particular existing slab outline.

An area laid with such slabs is better able to take wheeled vehicles if the slab has a flat face and a flat back. But if it is desired to have a relatively small total web surface visible at the top parts of the slab in the region of its face can be sunken. It is particularly advantageous to provide channel-shaped depressions between the first and/or second rows. These channel-shaped depressions preferably have in cross-section a bottom portion which corresponds to the form of an isosceles triangle with the apex directed upwards.

Particularly preferred fields of use for such slabs include the covering of areas of turf which after sowing have a substantially green effect and yet can be traversed by wheeled vehicles, and the covering of banks, more particularly river and lake banks and the like. Owing to the perforations in the slabs they are secured to the subsoil in a particularly secure manner. Of course it is possible to use the slabs to lay garage drives, Courtyards etc., and the perforations can be filled with gravel, asphalt, coloured ashes or the like.

Such slabs have many advantages resulting particu larly from the disposition of the rows of perforations obliquely to the sides of the base line of the slab. In practice slabs are laid with their longitudinal sides abutting a straight line boundary and where wheeled vehicles are driven over a covered area parallel or perpendicular to that boundary, the wheels mounted on a common axle will not simultaneously bear on perforations of a single row; this lessens the risk of heavy loading of areas of weak cross-section. Also the wheels will not then drive over consecutive perforations of a row and this lessens the risk of setting up powerful vibrations at certain speeds which might prove harmful to a vehicle suspension system. Furthermore when a vehicle is stationary there is less risk that both wheels of an axle will be in a recess at the same time which might impede drawing away when starting the vehicle and which would make it more difficult to push the vehicle. Also when such slabs are laid on banks bordering areas of water or water courses, the risk is lessened that a wave will break along a row of perforations floating soil out of many perforations simultaneously; hence the disposition of rows obliquely to the sides and ends of slabs is is likely to reduce erosion assuming of course that the sides or ends of the slabs extend horizontally.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be clearly understood and readily carried into effect several preferred forms will now be described by way of example only with reference to the accompanying drawings in which:

FIG. 1 shows in plan view a slab with round perforations which comprises at its outside recesses which occupy half or a quarter of the area of a perforation;

FIG. 2 shows in plan view a slab with square perforations and straight-sided recesses at the outline;

FIG. 3 shows in plan view a composite representation of slabs with round perforations and outline recesses, illustrative of a slab having a corrugated outline and of a slab having a zigzag outline;

FIG. 4 shows in plan view a slab similar to that shown in FIG. 2, but having in the top regions channel-like depressions between the first rows;

FIG. 5 shows a section taken on the line IX-IX of FIG. 4; and

FIG. 6 shows a section on the line X-X of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The outline of an interlocking slab l embodying the invention and shown in FIG. 1 can be regarded as having a notional base line that forms a rectangle covering two squares i.e. having sides twice as long as its ends are wide, with four corner points 6. The sides and ends of the slab l are formed of straight outline portions following a zigzag course, these portions being partly interrupted or cut into by recesses which will be described below. Beginning with the corner 6 at the lower left-hand portion of FIG. 1, a straight outline portion extends along a sixth of the base line longitudinal side outwards at an inclination, then this is followed by a straight outline portion 42 which extends inwards at an inclination along a sixth of the base line length, this portion at a half-way point on its length intersecting the longitudinal side constituted by the base line, then there follows a straight outline portion which extends outwards along a third of the base line length a halfway along its length intersects the base line and then there follows again an inwardly directed straight outline portion 42 extending along a sixth of the base line length, and, half-way along its length, intersecting the base line, and finally there follows a last straight outwardly directed outline portion which extends along a sixth of the base line length and ends at the left upper corner point 6 in FIG. 1. It will be realised that of these five straight outline portions just described the first, third and fifth in the series extend parallel to one another and also the second and fourth portions in the series are also parallel to one another, and the angles which the second and fourth portions form with the base line at this longitudinal side are larger than those of the first,

third and fifth outline portions. Owing to the pattern described there are formed at the longitudinal side of the slab two non-symmetrical projecting portions 22 and two non-symmetrical withdrawn portions 24. Also the outline form of the first half of the slab length is identically repeated along the second half.

The upper transverse end in FIG. 1 also has an identical repetition of one half of the longitudinal slab side, the corresponding outline portion being turned through 90. If this outline portion is turned through a further 90, the resultant shape is that of the outline of the upper half of the second longitudinal side of the slab, which can then be supplemented by again adding an identical profile to form a complete longitudinal side. Further turning of the lower half of the second iongitudinal side through 90 gives the outline of the lower end of the slab l in FIG. 1.

In the outline of the slab 1 formed by the straight outline portions described, recesses are provided comprising semi-circular recesses 32 at a half-way point on the longitudinal sides and quadrant-shaped recesses .34 at the four corners 6. If these recesses 32, 34 are disregarded therefore, the outlines of the longitudinal sides and the outlines of the transverse ends of the slab l are repeats of one another which would coincide upon side to side or end to end displacement.

One of the first rows 2 of circular perforations is situated on a diagonal between two corners 6, namely on a diagonal between the comers 6 from which the straight outline portions at the longitudinal sides of the slab extend obliquely outwards. Along this diagonal four perforations 10 are arranged which have a constant web width a. The web within between the respective outermost perforatons of this row and the recesses 34 which are situated adjacent in the row is also a. Two further first rows 2 extend parallel to the first row 2 just described, and the perforations 10 of these further first rows 2 have the same size as the perforations 10 of the first row 2 situated on the diagonal. These further first rows 2 include the semi-circular recesses 32 half-way along the longitudinal sides of the slab, whereby the spacing of the first rows 2 is defined. These further first rows 2 thus consist in each case of two perforations 10 having an intervening web width a, followed in each case by a semi-circular recess 32 again of a web width In this way a pattern of perforations l0 and recesses 32, 34 at the outline of the slab 1 is produced which comprises three first rows 2 and four second rows 4 situated at right angles to the first rows, the second rows each consisting of two perforations 10 and a corner recess 34 or a recess 32 situated centrally of the longitudinal side. At the places where the rows 2 or 4 intersect the outline of the slab devoid of any recess, the web width amounts in each case to /2 0; otherwise a web width a is also maintained in the second rows 4. The first rows 2 and the second rows 4 extend at an inclina' tion to the notional rectangular base line. The perfora tions designated as 10 inches in FIG. 1 are also situated in a straight line. But this line does not constitute a row in the sense of the present invention, since the web width along this line is greater than a.

The amount by which the projections and withdrawn portions 22 and 24 deviate from the base line can be so selected, with the outline described for the slab 1, that first straight outline portions 42, which are the portions described above as the second and fourth in the series,

are arranged parallel to the diagonal on which the central first row 2 is situated. Consequently, second straight outline portions 44 which represent the central outline portions of the transverse ends of the slabs I, extend parallel to the second rows 4 of perforations 10.

It will be realised that if the recesses at the outline are disregarded, the traces of the opposite sides and ends of the slab 1, upon parallel transposition would overlie and coincide with each other. As regards the perfora tions 10 and the recesses 32 and 34 there is symmetry about the centre point of the diagonal which contains a first row 2 of perforations 10. This central symmetry is also valid for the outline sides, having regard to the recesses 32 and 34.

it should be stressed that when using the usual methods of laying, such as for example a brickwork bond, wherein the slabs are laid with longitudinal side against iongitudinal side with an offset of half a side length, and herringbone formation wherein a transverse end is applied against a longitudinal side half starting from one corner, the recesses 32 and 34 supplement one another when slabs I are applied to form complete perforations 10, and when areas are completely laid out with the slabs a completely uniform constant pattern of perforations 10 is formed. The rows 2, 4 in the finished formation continue from slab to slab.

At the two lowest perforations 10' in FIG. 1 is shown that the perforations may also be conical. The perforations 10 can widen upwards or downwards.

The slab 1 shown in FIG. 2 represents a modification of the slab 1 described in connection with FIG. I. In this slab, the perforations 10 have a square basic shape, the webs being situated between sides parallel to one another of adjacent square perforations 10. The corner recesses 34 are produced by cutting off at straight lines the corners 6 of the slab I devoid of outline recesses, the outline form of the slab disregarding the recesses having been fully described in connection with FIG. 1, whereas the recesses 32 at the half-way point of the longitudinal sides of the slab are in the form of a square divided along its diagonal.

The other characteristics of the slab I described in connection with FIG. 1, such as the arrangement and number of perforations 10, the same web widths a everywhere in the row direction except for the webs between the last perforation l0 and the outline (if that region is devoid of any recess) the symmetry of the slab outline and of the perforations, and the edge recesses in a completed formation supplementing one another to form complete perforations, remain the same in this slab I also.

FIG. 3 shows in a single illustration two slabs I embodying the invention. The right-hand lower half is so arranged that, starting from the right-hand upper corner there is first of all situated at one longitudinal side a curved projecting portion 22 and then a congruent curved withdrawn portion 24, then again a congruent curved projecting portion 22 and finally a congruent corved withdrawn portion 24. The other longitudinal side is identical in form and can be produced by parallel transposition of the first side. The transverse ends each have an outline shape which corresponds to half a longitudinal side, starting from one corner. In this way the outline is always given a right angle at each corner.

Starting from this outline, quadrant-shaped recesses are provided at the corners as shown in FIG. I and semi-circular recesses at the half-way point of the longitudinal slab sides as shown in FIG. I. The perforations are cylindrical, all of the same diameter, and arranged like the perforations in the embodiment shown in FIG. I.

In the slab at the left and upper part in FIG. 3 the outline is formed from straight outline portions arranged along a zigzag course. There are two short portions of identical length next the corners of the longitudinal side of the slab and three straight portions situated between them, and also of identical length. The inclination of all the outline portions relatively to the base line length is identical. Therefore, here again the longitudinal outline side constitutes a repetition of the profile portion; the outline of the transverse end is brought about by turning one such portion through 90. Disregarding the recesses, opposite outline sides match on parallel transposition. At the corners quadrant-shaped recesses 34 are also provided and a semi-circular recess 32 half-way along the length of the slabv The illustrated arrangement of perforations I is also valid for the portion of a slab 1 shown at the left-hand upper regions in FIG. 3.

Cylindrical perforations are provided in the slab l in the same way as described in connection with FIG. 1, but the first rows 2 do not extend parallel to the first outline portions 42' and the second rows 4 are also not parallel to the second outline portions 44. This kind of pattern can also be achieved with a slab as shown at the left and upper sides in FIG. 3, if the extent of the projecting and withdrawn portions 22 and 24 respectively is made correspondingly large.

It will be understood that the two slabs l which are shown in FIG. 3 may also be provided with square perforations 10 as shown in FIGv 2 or with any other shape of perforations l0. Conveniently the recesses 32, 34 at the slab outline are then made to resemble the shape of the perforations 10, or the recesses are omitted.

The slab shown in FIGS. 4 to 6 is a modification of the slab shown in FIG. 2, channel-shaped depressions 71 being formed between the first rows 2 of perforations 10. In the region of the channel-shaped depressions 71, therefore, the top of the slab 1 has sunken portions so that the actual flat top 80 of the block 1 comprises only the webs between the perforations 10 of the first rows 2, which occupy the entire height of the slab l. The bottom of these channel-shaped depressions 71 comprises in cross-section the outline of an isosceles triangle with the apex situated above, so that in plan view there is an edge 72 in the middle of the channel-shaped depressions 71.

The slab 1 shown in FIGS. 4 to 6 thus has a considerably larger grassable surface. The groove shape for the depressions 71 described here afi'ords particularly good drainage for rainwater.

It should be pointed out that the outline of slabs embodying the invention can also be provided with a larger number of projecting and withdrawn portions than shown in the illustrations and can be made to a correspondingly larger size, so that one such slab can have a plurality of slabs as shown in FIGS. 1 to 6 laid abutting it.

The slabs embodying the invention can be made to any desired size. A size of about cm wide and 60 cm long is particularly useful; the thickness can be of the order of I2 cm for example. The slabs can conveniently be made by a normal cement casting or moulding process.

It should be pointed out that the outline of the slabs is preferably made centrally symmetrical, either disregarding the recesses or even taking them into account. Preferably when disregarding the recesses the opposite outline sides and ends of the slab reproduce one another by parallel transposition.

What I claim and desire to secure by Letters Patent 1s:

1. Perforated interlocking slab comprising in combination a face and a back bounded by an outline, said outline having portions that project and portions that are withdrawn with respect to a notional base line that forms a rectangle with opposite sides twice as long as its opposite ends are wide; said projections and withdrawn portions forming a matching pattern on said opposite ends and a matching pattern on each half length (regarded as extending from a corner) of said opposite sides of the slab whereby another like slab selectively oriented with its end abutting said half length and oriented with half the length of its side abutting said half length as may be desired interengages with said half length to prevent relative displacement longitudinally with respect to said half length; said perforations passing from said face to said back of the slab and being dis posed in first rows that extend parallel to each other and in second rows that extend at right angles to said first rows and parallel to each other, said first and second rows extending obliquely with respect to said rectangular base line.

2. Slab according to claim 1 wherein said first rows extend in the same direction as the diagonal of said rectangular base line.

3. Slab according to claim 2 wherein one of said first rows is situated on said diagonal.

4. Slab according to claim 1 comprising first straight line portions forming part of said slab outline and wherein said first rows extend parallel to said first straight portions of said outline.

5. Slab according to claim 4 comprising second straight line portions forming part of the said outline and wherein said second rows extend parallel to said second straight portions of said outline.

6. Slab according to claim 1 comprising at least one recess forming part of said slab outline of such shape and extent that the area of each said recess as seen in plan is equivalent to part of the area of said perforation.

7. Slab according to claim 6 wherein the area of each said recess is equivalent to at least one and not exceeding two quarters of the area of a said perforation.

8. Slab according to claim 6 wherein each said recess is so disposed in said pattern that when said slab is laid in abutment with other like slabs, adjacent recesses of neighbouring slabs combine to form a gap akin to a perforation.

9. Slab according to claim 1 wherein at least one rows of said first and said second rows are so disposed with respect to said pattern that when said slab is laid in abutment with other like slabs, said at least one rows are in alignment with the corresponding rows of neighbouring slabs.

I0. Slab according to claim I wherein consecutive said perforations of a said row are spaced apart by webs of even width.

11. Slab according to claim I0 wherein webs between said outline of said slab and the perforations nearest tions are tapered.

15. Slab according to claim I wherein said perforations are all of the same shape.

16. Slab according to claim 1 wherein parts of said slab in the region of its face are sunken relatively to said face.

* l I I UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION Patent No. 3,923,410 Dated December 2, 1975 REINHARD JORDAN and FRITZ VON LANGSDORFF Fritz von Langsdorff's interests assigned to F. von Langsdorff Bauverfahren GmbH of Rastaat, Germany.

It is certified that errors appear in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Heading, item [73] After "GmbH, Rastaat, Germany" insert --as to interests of Fritz von Langsdorff-.

Column 5, line 33, instead of "within" read -width.

Signed and Scaled this thirtieth D f March 1976 [SEAL] A nest.

RUTH C. MASON C. MARSHALL DANN Alresting Officer Commissioner ufParenls and Trademarks 

1. Perforated interlocking slab comprising in combination a face and a back bounded by an outline, said outline having portions that project and portions that are withdrawn with respect to a notional base line that forms a rectangle with opposite sides twice as long as its opposite ends are wide; said projections and withdrawn portions forming a matching pattern on said opposite ends and a matching pattern on each half length (regarded as extending from a corner) of said opposite sides of the slab whereby another like slab selectively oriented with its end abutting said half length and oriented with half the length of its side abutting said half length as may be desired interengages with said half length to prevent relative displacement longitudinally with respect to said half length; said perforations passing from said face to said back of the slab and being disposed in first rows that extend parallel to each other and in second rows that extend at right angles to said first rows and parallel to each other, said first and second rows extending obliquely with respect to said rectangular base line.
 2. Slab according to claim 1 wherein said first rows extend in the same direction as the diagonal of said rectangular base line.
 3. Slab according to claim 2 wherein one of said first rows is situated on said diagonal.
 4. Slab according to claim 1 comprising first straight line portions forming part of said slab outline and wherein said first rows extend parallel to said first straight portions of said outline.
 5. Slab according to claim 4 comprising second straight line portions forming part of the said outline and wherein said second rows extend parallel to said second straight portions of said outline.
 6. Slab according to claim 1 comprising at least one recess forming part of said slab outline of such shape and extent that the area of each said recess as seen in plan is equivalent to part of the area of said perforation.
 7. Slab according to claim 6 wherein the area of each said recess is equivalent to at least one and not exceeding two quarters of the area of a said perforation.
 8. Slab according to claim 6 wherein each said recess is so disposed in said pattern that when said slab is laid in abutment with other like slabs, adjacent recesses of neighbouring slabs combine to form a gap akin to a perforation.
 9. Slab according to claim 1 wherein at least one rows of said first and said second rows are so disposed with respect to said pattern that when said slab is laid in abutment with other like slabs, said at least one rows are in alignment with the corresponding rows of neighbouring slabs.
 10. Slab according to claim 1 wherein consecutive said perforations of a said row are spaced apart by webs of even width.
 11. Slab according to claim 10 wherein webs between said outline of said slab and the perforations nearest said outline are of a width half of said even width (save and except in the region of said recesses if there be any).
 12. Slab according to claim 1 wherein said perforations are circular as seen in plan view.
 13. Slab according to claim 1 wherein said perforations are square as seen in plan view.
 14. Slab according to claim 1 wherein said perforations are tapered.
 15. Slab according to claim 1 wherein said perforations are all of the same shape.
 16. Slab according to claim 1 wherein parts of said slab in the region of its face are sunken relatively to said face. 